Method for manufacturing lithiumnickel-manganese ferrite magnetic memory cores



United States Patent Ofiice 3,372,123 Patented Mar. 5, 1968 ABSTRACT OF THE DISCLOSURE A method of manufacturing magnetic core elements, useful as storage elements, and having a rectangular hysteresis loop, in which a mixture of lithium, nickel, manganese, and ferric oxides, after calcining, is compacted into annular cores which are heated to between 1200 C. and 1400 C. for not more than ten minutes in a water-free atmosphere.

elements are used, for example, in electronic computers.

When using magnetic cores as storage elements it is desirable to limit the occurrence of eddy currents as far as possible, so that magnetically soft, oxidic materials are used more andmore as raw materials for such cores, which materials have, as is well-known, a very low electric conductivity.

The suitability of such magnetic cores as storage elements is determined by their current pulse characteristics,

that is to say by their behaviour under current pulse conditions Very important in this connection is, for exrent pulse, has become maximum. This peak time is ample, the occurrence of a marked difference between the. zero-signal and the one-signal (in the computer techniques distinction is also made between the undisturbed one-signal, uVl, and the disturbed one-signal, rVl, ,but these magnitudes differ slightly in a good storage element). For this purpose, in addition to a sufficient rectangularity of the hysteresis loop, it is necessary that for a? given time of rise of the control current, the period which elapses between the beginning of the control current pulse and the moment at which the output 'voltage of the one-signal attains its maximum value is substantially; constant, For practical reasons the; beginning 'of the 'control current pulse is not used but the momentat which the control current reaches a strength of 10% of its maximum value-The term peak time (T ;of a magnetic core is then to be understood to mean the time which elapses between the instant at which the control cfurrent reaches a strength of 10% of its maximum valuefand the instant at which the output voltage of the one-signal, which is produced by the relevant control curnaturally dependent upon the time of rise (1,) of the control current pulse. In the experiments having led to the present invention, this time of rise was invariably 0.15 microsecond.

Variations in the control pulse characteristics of storage elements occurring due to temperature variations have mostly been corrected hitherto by varying the strength of the control current. Also the whole system of storage elements has been placed in a thermostaticallycontrolled enclosure to avoid interfering variations in temperature. However, such methods are complicated and laborious. Besides they are unusable, if during operation of the system, temperature differences occur between the individual storage elements because one element is switched over during a given period more frequently than another. It is therefore very important to have for disposal storage elements which not only exhibit.

a sutficiently great rectangular ratio of the hysteresis loop, but of which also the output voltage of the onesignal, as well as the peak time, are not dependent on temperature or to a small extent only within a wide range of temperatures (preferably between 40 C. and (3.).

In the experiments which have led to the present invention it has been found that magnetic cores consisting of lithium-manganese-(nickel) ferrites, within a range of compositions to be defined hereinafter and manufac-' tured by a method described hereinafter, have current pulse characteristics which render them highly suitable for use as storage elements.

The present invention relates to a method of manufacturing magnetic cores suitable for use as magnetic storage elements by sintering a mass of oxides of lithium, manganese, iron and possibly nickel, and/or compounds of said metals which change to the oxides when strongly heated, which mass has been molded before into the desired shape and, presintered at a temperature lower than 800 C., and it is characterised in that the relative quantitles of the said metals in the mass to be sintered, expressed in mol percent of the oxides Li O, MnO, Fe O and possibly NiO, are:

2.5 to 16.4 mol percent of Li O 0.3 to 68 mol percent of MnO 32 to 82 mol percent of Fe O 0 to 14 mol percent of NiO and that the sintering process takes place at a temperature from 1,200 C. to 1,40-0 C. in air or in a mixture of air and oxygen.

When magnetic cores manufactured in accordance with the invention are compared, as to their suitability for use as storage cores, with known magnetic cores consisting of manganese-magnesium-(zinic) ferrites, manganesecopper-(zinc) ferrites or lithium-manganese ferrites the following is found. Magnetic cores manufactured in accordance with the invention, if containing higher contents of manganese, are distinguished, with properties otherwise equivalent to those of the aforementioned known magnetic cores, by a strikingly high value of the output voltage of the one-signal. In the case of lower contents of manganese they have, as special favorable properties a very low temperature coefficient of the output voltage of the one-signal and a very low temperature coefficient What is claimed is:

1. A method of manufacturing a ferromagnetic ferrite core having a substantially rectangular hysteresis loop and a temperature coefiicient of the peak time and undisturbed one signal not greater than 0.65% per C. in a temperature range of at least +20 to +80 C. comprising the steps of, forming a mixture of about 2.5 to 16.4 mol percent of Li O; 0.3 to 68 mol percent of MnO; 32 to 82 mol percent of Fe O and up to 14 mol percent of NiO, presintering said mixture at a temperature not greater than about 750 C., finely-dividing the presintered mixture, compacting the finely-divided presin-tered mixture into an annular body and sintering said body at a temperature of about 1200 C. to 1400 C. for not more than minutes in an atmosphere containing at least as much oxygen as air and substantially free of water-vapor.

2. A method of manufacturing a ferromagnetic ferrite core as defined in claim 1, in which the quantity of NiO in the mixture is at least 3.2 mol percent.

3. A method as claimed in claim 2, in which the body after heating to a temperature from 1200" C. to 1400 C. is first cooled at a rate of at most 30 C. per minute to a temperature which is from 100 C. to 600 C. lower and then quenched.

4. A method as claimed in claim 2, in which the body 6 after heating to a temperature from 1200 C. to 1400 C. is cooled at a rate of more than C. per minute to a temperature which is from C. to 600 C. lower, maintained at this lower temperature for at least 5 minutes and the quenched.

References Cited UNITED STATES PATENTS OTHER REFERENCES Aghajanian: High Curie Temperature Square-Loop Ferrites, IBM Technical Disclosure Bulletin, volume 4, N0. 12, May 1962, page 85.

TOBIAS E. LEVOW, Primary Examiner.

R. D. EDMONDS, Assistant Examiner. 

